我试图为我的tableview附加一条消息，但它没有附加。请帮助我

Question

public static class StringBuilderExtensions
{
    /// <summary>
    /// Searches for the first index of the specified character. The search for
    /// the character starts at the beginning and moves towards the end.
    /// </summary>
    /// <param name="text">This <see cref="StringBuilder"/>.</param>
    /// <param name="value">The string to find.</param>
    /// <returns>The index of the specified character, or -1 if the character isn't found.</returns>
    public static int IndexOf(this StringBuilder text, string value)
    {
        return IndexOf(text, value, 0);
    }

    /// <summary>
    /// Searches for the index of the specified character. The search for the
    /// character starts at the specified offset and moves towards the end.
    /// </summary>
    /// <param name="text">This <see cref="StringBuilder"/>.</param>
    /// <param name="value">The string to find.</param>
    /// <param name="startIndex">The starting offset.</param>
    /// <returns>The index of the specified character, or -1 if the character isn't found.</returns>
    public static int IndexOf(this StringBuilder text, string value, int startIndex)
    {
        if (text == null)
            throw new ArgumentNullException("text");
        if (value == null)
            throw new ArgumentNullException("value");

        int index;
        int length = value.Length;
        int maxSearchLength = (text.Length - length) + 1;

        for (int i = startIndex; i < maxSearchLength; ++i)
        {
            if (text[i] == value[0])
            {
                index = 1;
                while ((index < length) && (text[i + index] == value[index]))
                    ++index;

                if (index == length)
                    return i;
            }
        }

        return -1;
    }

    /// <summary>
    /// Replaces the specified subsequence in this builder with the specified
    /// string.
    /// </summary>
    /// <param name="text">this builder.</param>
    /// <param name="start">the inclusive begin index.</param>
    /// <param name="end">the exclusive end index.</param>
    /// <param name="str">the replacement string.</param>
    /// <returns>this builder.</returns>
    /// <exception cref="IndexOutOfRangeException">
    /// if <paramref name="start"/> is negative, greater than the current
    /// <see cref="StringBuilder.Length"/> or greater than <paramref name="end"/>.
    /// </exception>
    /// <exception cref="ArgumentNullException">if <paramref name="str"/> is <c>null</c>.</exception>
    public static StringBuilder Replace(this StringBuilder text, int start, int end, string str)
    {
        if (str == null)
        {
            throw new ArgumentNullException(nameof(str));
        }
        if (start >= 0)
        {
            if (end > text.Length)
            {
                end = text.Length;
            }
            if (end > start)
            {
                int stringLength = str.Length;
                int diff = end - start - stringLength;
                if (diff > 0)
                { // replacing with fewer characters
                    text.Remove(start, diff);
                }
                else if (diff < 0)
                {
                    // replacing with more characters...need some room
                    text.Insert(start, new char[-diff]);
                }
                // copy the chars based on the new length
                for (int i = 0; i < stringLength; i++)
                {
                    text[i + start] = str[i];
                }
                return text;
            }
            if (start == end)
            {

                text.Insert(start, str);
                return text;
            }
        }
        throw new IndexOutOfRangeException();
    }
}